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Thursday, April 17, 2014

Variable Team Strength Ratings

At the beginning of the season when previewing teams I introduced something I titled "V-SRS," which was a tweak of basketball-reference's team rating metric, SRS, that adjusted a team's SRS based on how strong their opponent was. Basically, it tests the idea that some teams run up the score on weak teams or others are stronger versus the best teams in the league. With the playoffs coming, I thought this was the perfect time to try for an entire set of rankings based on "V-strength."

Quick description: the team rating (point diff.) column is just a basic team strength metric adjusted for the schedule, including back-to-back games. It's very similar to SRS. Strength variance is the degree to which a team's strength rating varies based on how good the opponent is. I've provided two columns to illustrate this: a team's rating versus a +3 team, which is a typical playoff team and one near 50 wins, and what a team's rating would be versus a +6 team, which is a strong contender as most title-winners are near +6 or over. Since the metric needs to be tested over multiple years still, I sorted teams by their strength versus +3 teams because it's a more conservative estimate of how good they are against competitive playoff teams.

When the media cite records of, say, the Spurs versus playoff teams, they're essentially doing a weak version of variable team strength. However, they do not adjust for schedule or the point differential of those games. Thus, the variable team strength metric, something I'm calling "V-strength" for now, more accurately reflects how good these teams are versus the top competition without completely disregarding all the other games and with an objective statistical adjustment.

One point here is that, yes, the Spurs were better against weak teams, though they rested their top guys so heavily that once the starters play more minutes the effect could be washed out. Also, I believe people are sleeping on the Clippers. They appear to play well against top competition, they're healthy at the right time, and they're being underrated because they're a new team on the big stage. The Mavericks and Bulls are two I would have thought of before crunching the numbers, as Dirk plays well in all situations and the Bulls have a top-notch defense and coaching to grind out wins versus better teams. The Heat, however, look worse, but perhaps with more playing time for Wade they'll punch at a higher weight class than their numbers indicate.

It's a new, untested metric, but it's good to quantify a natural question that's constantly arising -- how good are you against the best teams?

This is valuable information to look at. I second your view that people are sleeping on LAC but they are facing an extremely difficult road to the NBA Finals.

I made a thread on this on realgm: http://forums.realgm.com/boards/viewtopic.php?f=344&t=1316294

The hardest road to the NBA Finals since 1990 is the 01 Lakers who faced opposition with an average SRS of 6.17.

The potential road for LAC is far harder. If they land OKC and SAS in addition to GSW they will be facing an average competition of 6.60 with two of those series on the road. That is simply brutal competition. Even if they are the best team in the NBA they'll likely lose one of those series.

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One issue to keep in mind is sample size. You're dealing with an awful small sample size when you're talking +6 teams. There are only three of them so you're dealing with an awful small sample size.

No, it probably wasn't clear: I look at how every single team does versus the effect of increasing opponent strength. So how a team does versus a +6 one is an estimate based on a linear model of all the other teams. I don't only look at how a team does versus teams at +6 or higher.